Oscillation generator



Fab. 18, 19%. c, R, MOORE $1,747,837

050 ILLATI 0N GENERATOR Filed Aug. 5, 1925 Patented Feb. 18, 1930 UNITED STATES PATENT OFFICE CHARLES R. MOORE, OF MAPLEWOOD, NEW JERSEY, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK OSCILLATION GENERATOR Application filed August 5, 1925. Serial No. 48,223.

This invention relates to oscillation generators and more particularly to a method and means for generating currents of substantially constant frequency.

In oscillation generators, particularly those involving a mechanical vibrating memher, a common type being a tuning fork driven by an electromagnet energized by means controlled by the vibrations of the fork itself or by an external source, the current in the output circuit is distorted either in frequency or in wave form due to the mechanical imperfections of the vibrating system. One cause for this distortion is the unsymmetrical arrangement of devices, such as carbon transmitter buttons or other pickup elements, associated with the vibrating element. Another cause of distortion is the unsymmetrical properties of the various pick-up elements themselves.

An object of this invention is the production of an undistorted constant frequency current by means of an oscillating system including a mechanical vibrating element. A feature of the invention concerns the use of pick-up means symmetrically associated with the vibrating element.

This object and others, which will be apparent as the nature of the invention is disclosed, are accomplished in an oscillation generation system, employing a mechanical vibrating member as a frequency establishing means, by supporting the member at its nodal points and providing a symmetrical arrangement of the various driving and pick-up means in respect to the member- Although the novel features which are believed to be characteristic of this invention will be pointed out with particularity in the claims appended hereto, the invention itself, its objects and its advantages, the mode of its operation and the manner of its organization will be better understood by referring to the following description taken in connection with the accompanying drawing forming a part thereof, in which Fig. 1 is a plan view of an oscillation generating system constructed in accordance with this invention, and Fig. 2 is an elevation partly in section, showing one of the mountings including supports for the vibratin element.

Referring to Fig. 1 there is shown a vibrating element comprising a bar 1 capable of vibrating at a definite frequenc to establish the frequency of the generated oscillations. Bar 1 is pivotally mounted at its nodal points 2 in such manner that the bar is free to vibrate with an antinode at the center and an antinode at each end. This method of vibration is commonly referred to as free-free vibration. The theory of operation and the manner of arranging such a vibrating element in a frequency standard is disclosed in detail in U. S. patent to Ricker 1,543,124: issued June 23, 1925.

The driving element for bar 1 consists of an electromagnet 3 placed at the middle antinodal point. Electroma net 3 is actuated by current from source 9 owing through resistance 6 and switch 5, the current being va ried in amplitude in response to vibrations of the bar by means of pick-up element 4 of -the carbon transmitter button t pe mounted at the middle antinodal point of the bar and opposite electromagnet 3. The amplitude of the vibrations and consequently the amount of current in the output circuit L, is varied by means of resistance 6.

Current in the circuit including microphones 7, resistances 10, primary of transformer 8 and battery 9, is varied by means of pick-up elements '7 placed at the two ends of the bar, but on opposite sides thereof. The secondary of transformer 8 is connected to the work circuit L, through which the oscillations generated may be transmitted to suitable translating devices. Obviously the oscillations may be amplified if desired. Resistances 10 serve to stabilize the output circuit by providing a constant resistance in series with the microphones resistances. These resistances may be included in the coil primary, if desired.

Each of the various pick-up elements 4 and 7 comprises a variable resistance element 20 pressed lightly against the bar 1 and supported by standard 22. The light pressure allows the bar to move freely in response to the driving force and introduces a minimum amount of damping to the vibrations, whereby a pure and undistorted wave is produced- I pointed fulcrum members 11 and 12, between which the bar is clamped. A pointed fulcrum is desirable in order to reduce friction to a minimum, and to allow free and unimpeded movement of the vibrating element or bar. This type of mounting is preferred over that including, for example, a knife-edge bearing on which the bar rests, since it insures that the fulcrum points are nearer the neutral' plane of fiexure of the bar so that there is less relative movement of the bar and its supports at their points of contact. This, of course, results in less damping and hence tends to increase the purity of the resultant wave form.

Vibratory condition of the bar may be initiated by closing the switch 5. As the bar vibrates the resistance of the transmitter button 4 is caused to vary in synchronism therewith. A current of corresponding frequency is thereby produced in the driving circuit including the magnet 3 the flux of which is caused to vary at the same rate to maintain the bar vibrating at its resonant frequency.

The transmitter buttons 7, being associated at antinodal points on opposite sides of the bar, will have their resistances varied at the same rate and will cause current variations of the resonant frequency of the bar to flow "through the two halves of the primary winding 0 the transformer 8.

Since the transmitter buttons 7 are on opposite sides of the bar 1, the movement of the bar will cause the resistance of one button to decrease and the resistance of the other to increase with the result that the change of current in the two halves of the primary winding of transformer 8 will be opposite in sign.

If the two buttons have the same characteristics and are exactly symmetrically positioned with respect to the bar, the modes of variation of the currents therein will be identical, although the variations will be of respectively opposite phase. The two halves of the primary winding of transformer 8 are wound in the same direction looking along their common axis.

These various relationships insure that the consecutive alternations of the current in the secondary of transformer 8, and therefore in the work circuit L, will be exactly symmetrical, each bein made up by a superposition of the effects 0 an increase in the resistance tween consecutive alternations of a wave identifies a condition of entire absence of even harmonics. Since the distortions, characteristic of the wave generated in each button individually, in general, result from the presence of even harmonics, the symmetry results in the production of a substantially pure sine wave.

A comparable symmetry cannot be obtained when using a single button. It obviously cannot if such a button is operated about a point near the foot of its characteristic curve (plotted between change of dimension of the button and change in resistance) and a button cannot, as a practical matter, be operated about a point of inflection of such a characteristic curve where an approximateconditionof symmetry could theoretically be attained, without too greatly damping the movement of the bar. With the arrangement disclosed, an exact symmetry can of the curve, so long as the same points are chosen for the curves of both buttons.

The operational features above described, as relating to a particular type of pick-up device, apply equally well to other pick-up devices which are characterized by a nonlinear relation of their input and output quantities. The relationship of the two buttons and their associated circuits is functionally the exact equivalent of the arrangement illustrated, for example, in Fig. l of U. S. patent to Colpitts No. 1,128,292, February 16, 1915, in which the space circuits simulate the buttons, herein disclosed, the impedances of which are varied by corresponding variations of pressure or movement, while in the Colpitts system the variations are produced by changes in the grid otentials. The arrangement, however specifically applied, is identified in the minds of those skilled in the art by the term push-pull. i

The driving means and pick-up means may be reversed in position or in general, the bar'may be driven from any antinodal point and the pick-up means placed at any other antinodal points without altering the operation of the system. The bar may also be supported at more than two places to produoe other types of free-free vibrations having more than three antinodal points in which case the bar can be caused to vibrate at high frequencies.

The oscillator is of a simple mechanical construction and requires practically no adjustment when moved from one place to another to be used in connection with other apcordance with the scope of the invention as defined by the following claims.

What is claimed is:

1. An oscillation generator comprising an elastically vibratory element and associated driving means, in combination with a pair of pick-up devices associated in energy-transfer relation to said element and connected to an output circuit in push-pull relationship.

2. An oscillation generator com rising a bar supported so as to produce rec-free vibrations, driving means adapted to cooperate with the center of said bar, and current controlling elements adapted to be actuated by the movement of the ends of said bar, said controlling elements being mounted upon opposite sides of the bar.

3. In an oscillation generation system, an elastically vibratory element, means for'driving said element and current controlling elements actuated by the vibrating element, said controlling elements being mounted in opposing relationship with respect to the vibrating element.

4. In an oscillation generation system, a vibrating bar supported at its nodal points havin antinodes at its middle and at its two ends, riving means associated with said bar at one of its antinodal oints, and current controlling devices at tli points of said bar and mounted in opposing relationship with respect thereto.

5. A frequency standard comprising a bar vibrating in free-free 'gelationship, means for drivin said bar comprising an electromagnet and a variable resistance device associated with the middle of said bar, and current pick-up devices mounted at the two ends of said bar in opposing relationship thereto, said pick-up devices bein connected to the output circuit in push-pul relationship.

6. In combination a continuously vibrating mechanical element, a plurality of circuit controllin devices controlled thereby, said devices being so related to said vibrating element as to be simultaneously aflfected thereby in opposite sense, an output circuit, and a means for translating the currents in said devices jointly into alternating current in said output circuit, said means being ada ted to afiect said output circuit cumu ative y with respect to odd harmonics of the current in said devices, including the fundamental, and differentially with respect to even harmonics of said current.

7. A frequency standard comprising a. bar vibrating in free-free relationship, means for setting said bar into vibration in accordance with electrical variations, and current pick-u elements mounted at the two ends of sai bar in opposin relationship thereto,

said pick-up elements eing connected to the output circuit in push-pull relationship.

8. An oscillation generator com rising a. bar supported so as to produce ee-free e other antinodal- 

